1. Field of the Invention
The present invention generally relates to an image display apparatus, and particularly relates to a liquid crystal display apparatus.
2. Description of the Related Art
In a liquid crystal display (LCD) panel, pixels each including a transistor are arranged in matrix form, with gate bus lines extending in the horizontal direction being connected to the gates of the pixel transistors, and data bus lines extending in the vertical direction being coupled to the pixel electrodes of the pixels via the transistors. Each pixel electrode is positioned to face a common electrode (opposite electrode) across a liquid crystal layer, thereby forming a condenser corresponding to each pixel. When data is to be displayed on a liquid crystal panel, the gate driver drives the gate bus lines one after another so as to make the transistors conductive for one line, and the data driver writes data for one horizontal line to the pixels simultaneously via the conductive transistors.
In order to display a desired image by writing display data at proper timing to the liquid crystal panel having the configuration as described above, a timing controller is provided in the liquid crystal display apparatus. This timing controller receives a clock signal, display data, and a display enable signal indicative of the timing of the display position from an apparatus on the host side (television tuner, computer, or the like). The timing controller counts the clock pulses of the clock signal starting from a rise of the display enable signal so as to determine timing in the horizontal position, thereby generating various control signals. The timing controller also counts the number of display enable signals so as to determine timing in the vertical position, thereby generating various control signals. The timing controller further detects the portion of the display enable signal at which the LOW period continues for more than a predetermined number of clock pulses, thereby detecting the position of the start of each frame.
In general, all that such liquid crystal display apparatus does is display the display data supplied from the host apparatus based on the timing signals supplied from the host apparatus. Accordingly, when the host apparatus hangs-up, for example, resulting in its display data being frozen, the liquid crystal display apparatus continues to display the frozen display data supplied from the host side. In this case, it is impossible to distinguish between a state in which display data of proper operation does not show any change and a state in which the display data is frozen due to operation failure.
If frozen display data as described above continues to be displayed in a system relating to the operation of a ship or the like, for example, decisions and determinations for the operation are made by mistake based on the information displayed on the display screen that is being frozen. Such a situation may lead to grave consequences in which human lives may be lost. It is thus unacceptable to fail to detect an abnormal state.
[Patent Document 1] Japanese Patent Application Publication No. 5-053541
[Patent Document 2] Japanese Patent Application Publication No. 5-056374
Accordingly, there is a need for a liquid crystal display apparatus that can detect a freeze state of the display data if the display data supplied from a host apparatus is frozen.